Terephthalate polyesters like polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are thermoplastic polymers that have been widely used in the plastic industry, especially for the preparation of films, fabrics, plastic containers of all kinds, textile materials and the like in the case of PET and for the preparation of auto body panels, fenders, relays, iron handles, lawn mower housings and the like in the case of PBT. However, with the growing use of terephthalate polyesters products also came the waste disposal problems and expenses encountered by both the manufacturers and the users.
There is at present a certain number of avenues available to recycle or degrade terephthalate polyesters. For example, high molecular weight polymer PET has been recycled by either grinding solid scrap PET and using the ground material as a filler or by partially depolymerizing the high molecular weight polymer in the presence of a monomer to produce a low molecular weight polymer. These types of processes are disclosed in U.S. Pat. No. 3,037,048.
In U.S. Pat. No. 3,037,048, Lotz discloses a process through which scrap PET products such as filaments, films, fabrics and others are recycled to regenerate the compound dimethyl terephthalate (DMT). This process involves the depolymerization of PET and transesterification in the presence of methanol to yield DMT.
Furthermore, U.S. Pat. No. 4,578,502 issued to Cudmore discloses the use of PET scrap for recovering ethylene glycol and either terephtalic acid or dimethylterephthalate. The process includes depolymerization of a slurry of scrap PET by hydrolysis or methanolysis, and subsequently crystallization of the desired product. The disclosure of U.S. Pat. No. 4,578,502 is limited to the production of dimethyl terephthalate. In fact, at column 3, lines 22-28 of this document, it is stated that it is preferable not to use alcohols of a higher molecular weight than methanol.
Thus, most of the PET recycling processes using transesterification presently known in the art are mainly aimed at producing starting materials that could be used for the synthesis of new PET products. Therefore, it would be interesting to provide a one step process for the recycling of PET that would yield a product that could be readily used either in the plastics industry or otherwise. Plasticizers are a good example of useful and readily usable products for the plastics industry.
Plasticizers are crucial constituents in the preparation of some plastic products. For example, di octyl terephthalate (DOTP) is particularly useful to the PVC industry. Esters of this type can be synthesized mainly by reacting terephthalic acid with a suitable alcohol. Unfortunately, in this case, the esterification reaction is very slow, thereby making the process economically undesirable. Alternatively, the transesterification of di methyl terephthalate to DOTP through its reaction with 2-ethyl hexanol is an interesting reaction that yields DOTP rather quickly.
Terephthalate polyesters are polymers that are widely used in the plastics industry despite the serious disposal and recycling problems encountered by their users. Therefore, suitable recycling alternatives that would yield a product of good commercial value would be highly desirable.